This invention relates generally to sifters for separating coarse and fine feed materials and more particularly to an improvement to such sifters allowing adjustment of agitator blades to accommodate different feed materials and different size distributions of such materials.
Current horizontal cylindrical sifters have non-adjustable agitator blades usually fixed to non-adjustable arms and oriented axially within the cylindrical screen of the sifter. Such fixed blades can handle some product capacities better than others at a given speed. Although performance and capacity can be improved by speed adjustments, it is not economical to change speed for different products. The result may be rotor speed which is too high and which causes product overflow and high fines content in the sifted product.
Operation of a typical horizontal cylindrical sifter includes feeding the ground grain material having a full distribution of particle sizes into the inlet of the sifter housing. The mixture lands on the cylindrical screen where it is rabbled or stirred by agitator blades attached by agitator arms to a rotating shaft longitudinally disposed within the screen. The stirring action allows the fine particles to separate from the coarse particles and to fall through the screen into a fines chamber surrounding the screen in the sifter housing. The coarse particles are retained on the screen and, due to the displacement action of new mixed material entering the sifter inlet, is discharged through the coarse particle outlet. Depending on the properties of the material being processed, straight longitudinal orientation of the agitator blades may be most efficient at a given rotor speed. However, there are many cases in which this will not be so and in which it may be necessary to provide some additional driving force to move the coarse particles to the outlet. Co-current blowers or other air conveyors have the disadvantage of moving fines faster than coarse particles to the outlet, thereby defeating the sifting operation. Countercurrent blowers are much harder to control and to balance the elutriative effect on fines, which may cause rejection of fines out through the inlet.
The foregoing illustrates limitations known to exist in present horizontal cylindrical sifters, and it would be advantageous to provide an alternative directed to overcoming one or more of those limitations. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.